The present invention relates to an electronic shutter driving device for a camera.
In general, the electronic shutter driving devices include a logarithmic compression circuit and a logarithmic expansion circuit. The logarithmic expansion circuit generally consists of transistors or field-effect transistors. The operation of semiconductor elements is greatly influenced by the temperature variation and their temperature coefficients vary widely depending on temperatures.
The conventional logarithmic expansion circuit including operational amplifier generally requires two power or voltage sources. There has been also a circuit in which the noninverting input terminal of an operational amplifier is not grounded or not impressed with a source voltage, but is connected to a center tap of a voltage divider. However the input or output voltage range is limited by a voltage at the center tap, so that the input signal processing range is reduced and consequently the satisfactorily precise control of the shutter driving circuit cannot be attained. Therefore one-power-source type logarithmic expansion circuit cannot be employed in the camera which requires precise operation. The logarithmic expansion circuit operable with two power sources has a defect that the shutter driving device becomes heavy in weight.